1. Field of the Invention
The present invention relates to a spread illuminating apparatus, and more particularly to a spread illuminating apparatus used as an illuminating means for a liquid crystal display device.
2. Description of the Related Art
A liquid crystal display (hereinafter referred to as xe2x80x9cLCDxe2x80x9d) which is low in profile, small in occupied volume, and lightweight has been extensively used in electric products including personal computers and cellular phones, and the demand therefor has been increasing. However, since a liquid crystal used for the LCD does not emit light by itself, it is necessary to provide a separate illuminating apparatus besides the LCD in order to irradiate a liquid crystal when the LCD is used in dark places where sunlight or room light is not fully available. Thus, the illuminating apparatus for irradiating the liquid crystal is desired to be compact and small in power consumption, and a low profile spread illuminating apparatus of side light type (light conductive plate type) is often used recently.
FIG. 4 is an exploded perspective view showing a conventional spread illuminating apparatus 1xe2x80x2 of side light type in which a spot-like light source is mounted on a flexible printed circuit (hereinafter, referred to as xe2x80x9cFPCxe2x80x9d).
As shown in the figure, the spread illuminating apparatus 1xe2x80x2 generally comprises a light conducive plate 2 made of a light-transmissible material, lamps 5a and 5b comprising light conductive bars 3a and 3b and spot-like light sources 4a and 4b, respectively, and arranged respectively along end surfaces 8 and 18 of the light conductive plate 2, an FPC 6 on which the spot-like light sources 4a and 4b are mounted, and light reflection members (lamp frames) 13a and 13b covering the lamps 5a and 5b. Light rays emitted from the lamps 5a and 5b and introduced into the light conductive plate 2 are reflected therein so as to irradiate an LCD (not shown) disposed under the light conductive plate 2.
The light conductive plate 2 has a light reflection pattern 29 on a top surface (observation-side surface) 25 thereof so as to uniformly spread the light rays introduced thereinto through the end surfaces 8 and 18 toward the LCD entirely through a bottom surface 26. The light reflection pattern 29 comprises a plurality of grooves 27 and a plurality of flat portions 28 each present between adjacent grooves, and is oriented parallel to the length direction of the light conductive bars 3a and 3b. Alternatively, the light reflection pattern 29 may comprise only grooves continuously arrayed, and the grooves do not have to be parallel with the length direction of the light conductive bars 3a and 3b but may be oriented to have a predetermined angle thereto. With the light reflection pattern thus constructed, the light rays having entered the light conductive plate 2 are substantially uniformly reflected at the whole top surface of the light conductive plate 2 thereby uniformly irradiating the LCD disposed under the light conductive plate 2.
As above described, the lamps 5a and 5b are composed of the light conductive bars 3a and 3b and the spot-like light sources 4a and 4b (for example, light-emitting diodes), respectively. The light conductive bars 3a and 3b have optical path conversion means 12a and 12b, respectively, formed on one side surface thereof opposite to a side surface facing the light conductive plate, and have the spot-like light sources 4a and 4b, respectively, disposed close to an end surface thereof. The spot-like light sources 4a and 4b are mounted by soldering at land portions formed on the FPC 6. The land portions are electrically connected to a power source pattern (not shown) formed on the FPC 6, and power is supplied to the land portions from a connect section 6a of the FPC 6 via the power source pattern.
The lamp frames 13a and 13b are provided so as to cover the lamps 5a and 5b, respectively, thereby allowing light rays emitted from the spot-like light sources 4a and 4b to efficiently enter the light conductive plate 2, preventing the light conductive bars 3a and 3b from being damaged by contact with any other members, and making the light conductive bars 3a and 3b further dustproof. The lamp frames 13a and 13b are shaped substantially like U-letter, and cover respective longitudinal surfaces of the light conductive bars 3a and 3b except respective surfaces facing the light conductive plate 2, and cover also both end portions of the light conductive plate 2. The lamp frames 13a and 13b are each formed of a hard resin member, on inner surface of which a film with a metal such as silver vapor-deposited or a white film is adhered or formed of a bent metal sheet such as an aluminum sheet, a stainless steel sheet, or the like.
FIG. 5 is a schematic view showing how light rays emitted from a spot-like light source are guided into a light conductive plate.
The light rays radially emitted from the spot-like light source 4 are reflected and refracted at four side surfaces of the light conductive bar 3 substantially rectangular in section or by the lamp frame 13 covering the longitudinal surfaces of the light conductive bar 3, and most of the light rays are guided to the light conductive plate. More specifically, as shown in the figure, some light elements 7a and 7b enter the light conductive bar 3 through the end surface thereof, and are confined therein due to a difference in the refractive index between the light conductive bar 3 and the atmosphere. Then, the light elements 7a and 7b are guided into the light conductive plate 2 after being reflected and refracted at grooves 14 of an optical path conversion means. But, some light elements such as an element 7c do not enter the light conductive bar 3, and directly enter the light conductive plate 2. This occurs if members are not appropriately assembled, specifically, if there is too much space between the spot-like light source 4 and the end surface of the light conductive bar 3. When this occurs, a linear bright line appears on a screen.
Another factor for generating a bright line on the screen will be described with reference to FIG. 6. In the figure, the members making up the spread illuminating apparatus are correctly and accurately positioned and assembled. In such a state, when the light conductive plate 2 is observed from a left-to-right direction (a direction parallel to the grooves 27 of the light reflection pattern 29 formed on the light conductive plate 2), a zonal bright line indicated by a reference numeral 7d, so-called reflected bright line, appears on an end surface 15 of the light conductive bar 3 due to reflection at the grooves 27 and reflection at the bottom surface of the light conductive plate 2 (Fresnel reflection).
The spot-like light sources 4a and 4b need to be arranged right in font of and close to the end surfaces of the light conductive bars 3a and 3b, respectively, in order to allow light rays to efficiently enter the light conductive bars 3a and 3b. According to the prior art shown in FIG. 4, the spot-like light sources 4a and 4b are mounted on the FPC 6 as shown in FIG. 7. Accordingly, when the spot-like light sources 4a and 4b are disposed close to respective end surfaces of the light conducive members 3a and 3b, parts of the FPC 6 (shaded area) are located under the end portions (bottom side) of the light conductive bars 3a and 3b as shown in FIG. 8. In this case, since the FPC 6 has, for example, a yellow color, an orange color, or the like, when light rays radially emitted from the spot-like light sources 4a and 4b are partly reflected at the FPC 6 and enter the light conductive plate 2, a bright line of the color of the FPC 6 appears on the screen due to the reflected light rays. This phenomenon is conspicuous, in particular, when the members are not correctly positioned to be assembled thereby generating the linear bright line on the screen, or when the zonal reflected bright line appears, as described above.
The present invention has been made in light of the above problems. Accordingly, it is an object of the present invention to provide a spread illuminating apparatus which is fire from the bright line of the color of the FPC appearing on a screen.
In order to achieve the above object, a spread illuminating apparatus according to the present invention comprises: a light conductive plate made of a light-transmissible material; at least one lamp including a light conductive bar disposed close to and along an end surface of the light conductive plate and at least one spot-like light source arranged at an end surface of the light conductive bar; and an FPC having the spot-like light source mounted at land portions thereof, the land portions being positioned such that the FPC does not exist ahead of a light emitting surface of said spot-like light source mounted.
According to the configuration of the present invention, light rays emitted radially from the light emitting surface of the spot-like light source does not irradiate the FPC and therefore light rays of the FPC color do not enter the light conductive bar.
In order to achieve the above object, in the spread illuminating apparatus according to the present invention, preferably, the FPC having the spot-like light source mounted thereon does not overlap any part of a top surface or a bottom surface of the light conductive bar when the spot-like light source is set in place at the end surface of the light conductive bar.
According to the configuration of the present invention, light rays having entered the light conductive bar do not irradiate the FPC and light rays of the color of the FPC color do not enter the light conductive plate.